This invention is in the area of the manufacture of MEMS (microelectromechanical systems) as well as semiconductor devices, or any other devices that require removal of a material relative to a substrate or other deposited material. In particular, this invention addresses gas-phase etching procedures, with particular emphasis on etching pressure with a preferably spontaneous chemical etchant as well as detection of the end point in an etching process, use of diluents, recirculation of etchant gas, and/or other additional features set forth below. The invention is also directed to apparatus for implementing one or more of these method features. “MEMS”, “microelectromechanical” and “micromechanical” are used interchangeably throughout this application and each may or may not have an electrical component in addition to the microstructure component.
The use of etchants for removing sacrificial layers or regions in a multilayer structure without removal of an adjacent layer or region is a necessary and common step in the manufacture of semiconductor and MEMS devices. The MEMS devices of the present invention can be devices for inertial measurement, pressure sensing, thermal measurement, micro-fluidics, optics, and radio-frequency communications, with specific examples including optical switches, micromirror arrays for projection displays, accelerometers, variable capacitors and DC or RF switches. If a semiconductor device is etched, it can be any device that is made of or has on a substrate a material that is to be removed with a preferably gas phase chemical etchant.
The success of an etch step in the manufacture of microstructures is improved not only due to the selectivity of the etchant, but also due to the ability to accurately determine the end point of the etching process. Isotropic etching is of particular interest in processes where the purpose of the etch is to remove a sacrificial layer that is intervening between functional layers or between a functional layer and a substrate. Gas phase etchants, particularly in the absence of plasma, are desirable for isotropically removing a sacrificial layer.
The method of the present invention is useful for producing semiconductor devices and deflectable MEMS elements (deflectable by electrostatic or other means) which, if coated (before or after gas phase processing) with a reflective layer, can act as an actuatable micromirror. Arrays of such micromirrors can be provided for direct view or projection display systems (e.g. projection television or computer monitors), as well as for optical switching. The present invention is also adaptable to etching microfabricated devices other than deflectable MEMS devices (e.g. semiconductor based devices, carbon nanotubes on glass, nondeflectable MEMS devices such as sensors, etc.).